Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, elevate, coagulate or cauterize tissue, or to separate muscle tissue off bone. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from an ultrasonic transducer, through a transmission component or waveguide, to the surgical end effector. Such instruments may be used for open or minimally invasive surgical procedures, such as endoscopic or laparoscopic surgical procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the single or multiple-element end effector of such instruments at ultrasonic frequencies induces longitudinal, transverse or torsional vibratory movement that generates localized heat within adjacent tissue, facilitating both cutting and coagulation. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting, coagulating, scraping, or lifting tissue with or without the assistance of a clamping assembly.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic transmission component such as a waveguide extending from the transducer section to the surgical end effector. The waveguides and end effectors are most preferably designed to resonate at the same frequency as the transducer. Therefore, when an end effector is attached to a transducer the overall system frequency is the same frequency as the transducer itself.
The zero to peak amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:    ω=the radian frequency which equals 2π times the cyclic frequency, f and    A=the zero-to-peak amplitude.
The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2A.
Solid core ultrasonic instruments may be divided into two types, single element end effector devices and multiple-element end effector. Single element end effector devices include instruments such as blades, scalpels, hooks and/or ball coagulators. Multiple-element end effectors may include a mechanism to press tissue against an ultrasonic blade. Multiple-element end effectors comprise clamping scalpels and/or clamping coagulators or any combination of a clamping assembly with a single element end effector. Multiple-element end effectors may be employed when substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. Ultrasonic clamp coagulators, for example, may be employed for cutting and coagulating tissue, particularly loose and unsupported tissue. Multiple-element end effectors that include an ultrasonic blade in conjunction with a clamp apply a compressive or biasing force to the tissue to promote faster coagulation and cutting of the tissue.
Ultrasonic clamp coagulators provide an improved ultrasonic surgical instrument for cutting/coagulating tissue, particularly loose and unsupported tissue, wherein the ultrasonic blade is employed in conjunction with a clamp for applying a compressive or biasing force to the tissue, whereby faster coagulation and cutting of the tissue are achieved.
Ultrasonic instruments are designed and manufactured such that the maximum amplitude of the longitudinal ultrasonic vibration (i.e., the anti-node) is localized at or near the distal end of the end effector in order to maximize longitudinal excursion of the distal end. The active length of an ultrasonic instrument is generally defined as the distance from the distal end of the end effector (where ultrasonic displacement is at a maximum) to a proximal location along the end effector where ultrasonic displacement decreases below a predetermined level approaching a node (where ultrasonic displacement is at a minimum). The length segment of an end effector surrounding a node where ultrasonic displacement is below a predetermined level is defined as the nodal gap. Accordingly, the nodal gap is the length in the vicinity of the node that has insufficient displacement to generate the necessary heat for efficient and/or effective cutting and/or coagulation.
As used herein, the term “nodal gap” refers to the length segment of an end effector that has insufficient ultrasonic displacement to generate the necessary heat for efficient and/or effective cutting and/or coagulation. As used herein, the term “nodal gap region” refers to the area in the vicinity of a node and may refer to the area on or in an end effector or the area adjacent to the end effector in the vicinity of a node. As used herein, the term “nodal energy gap” refers to the condition where insufficient ultrasonic displacement to generate the necessary heat for efficient and/or effective cutting and/or coagulation is produced in the vicinity of a node.
The relatively low displacements in the vicinity of the node result in lower amounts of heat being delivered to tissue in contact with the end effector in the nodal gap region than in other regions of the end effector. Accordingly, in the nodal gap region, the tissue in contact with the blade does not get directly heated. As a result, the tissue is not effectively cut and/or coagulated, and the tissue may stick to the end effector in the nodal gap region or may simply be desiccated without being transected. It would be desirable to provide an end effector for use in an ultrasonic surgical instrument that effectively eliminates the nodal gap.